1. Field of the Invention
The present invention relates to a communication apparatus and a method for determining connection.
2. Description of the Related Art
ErP Directive Lot 6 as an energy-saving standard in Europe has been revised. When a network line including a facsimile (FAX) and a device become a non-communication state, no job comes from a network or a FAX line, and a multifunction peripheral (MFP) or the like having communication functionality is not used until a user directly operates and uses the device such as copying or scanning next time. For this reason, the standard has been revised so as to make the device an off-mode state when the network line including a FAX is in a non-communication state.
In a FAX public line, a voltage is applied across lines by station power supply from a telephone station, and whether the FAX public line and the device are connected to each other can be determined by causing a FAX line control device that controls the FAX line to detect a voltage value between the lines.
However, recently, as a result of seeking a further energy-saving effect, even the FAX line control device turns off electric power. A technique is known that provides a ringing detection circuit to detect an incoming call (a ringing signal) from the FAX line and polarity inversion during energy-saving, monitors a voltage between the lines, detects the incoming call and the polarity inversion, and also detects line disconnection by this circuit.
Japanese Patent Application Laid-open No. 2013-225840 discloses a communication terminal that is connected to a public line and includes facsimile functionality, the communication terminal including a mechanical relay that switches between a disconnected state in which an external telephone connected to the communication terminal is disconnected from the public line and a connected state in which the external telephone is connected to the public line, a polarity inversion detection circuit that detects whether the polarity of a signal from the public line has been inverted, and a line controller that is set with non-ringing receiving functionality that allows reception without ringing the external telephone in response to ringing from the public line and controls the mechanical relay so as to switch from the connected state to the disconnected state when inversion of the polarity of the signal from the public line is detected.
However, the conventional ringing detection circuit includes a capacitor mounted in between the lines to detect ringing. Electric charge is charged to this capacitor by the station power supply, and even when line disconnection occurs, the state in which the electric charge is charged to the capacitor continues for a while, and the voltage between the lines remains to be maintained. The electric charge of the capacitor then escapes through natural discharge. The ringing detection circuit includes a photo coupler and ringing and polarity inversion can be detected from a value of current flowing through the photo coupler. However, the ringing detection circuit has a problem in that, from a value of current flowing through the photo coupler caused by a voltage decrease caused by natural discharge, the voltage decrease cannot be detected due to the characteristics of the photo coupler, and consequently, line disconnection cannot be detected.
In view of the above, there is a need to provide a communication apparatus and a method for determining connection that can detect line disconnection when a line is in a non-communication state.